| Current Conditions | ||
| Temp |  | -2.6 C |
| RH | | 96 % |
| Wind | | NW 23 mph |
| Road | | Closed |
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Hawaiian Islands Synoptic Discussion and Guidance 292 FXHW60 PHFO 010632 AFDHFO AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE HONOLULU HI 830 PM HST SAT FEB 28 2015 .UPDATE... THUNDERSTORMS HAVE BEEN FLARING OVER PORTIONS OF MAUI AND THE BIG ISLAND WITH ADDITIONAL HEAVY SHOWERS AND THUNDERSTORMS EXPECTED TO POP UP ACROSS THE EASTERN END OF THE STATE THROUGH THE NIGHT. THE FORECAST IS ON TRACK THIS EVENING...AND THE PREVIOUS DISCUSSION BELOW CAPTURES THE SCENARIO QUITE WELL. && .SYNOPSIS... A NORTH TO SOUTH ORIENTED SURFACE TROUGH IS LOCATED NEAR THE BIG ISLAND. MOISTURE ALONG THIS BOUNDARY COMBINED WITH INSTABILITY ALOFT DUE TO AN UPPER TROUGH WILL CONTINUE TO PRODUCE LOCALLY HEAVY DOWNPOURS AND THUNDERSTORMS ACROSS MAUI TONIGHT AND THE BIG ISLAND INTO MONDAY. TRADE WINDS WILL SPREAD ACROSS THE STATE ON LATER THROUGH SUNDAY AS THE TROUGH WEAKENS...BUT LINGERING ENHANCED MOISTURE AND INSTABILITY WILL REMAIN NEAR THE BIG ISLAND OVER THE NEXT SEVERAL DAYS. && .PREV DISCUSSION 400 PM... A WEAKENING SURFACE TROUGH WITH A NORTH-TO-SOUTH AXIS IS LOCATED NEAR THE BIG ISLAND. MEANWHILE...AN UPPER LEVEL TROUGH IS LOCATED TO THE NORTH NORTHWEST OF HAWAII WITH THE BASE OF THE UPPER TROUGH OVER THE WESTERN END OF THE STATE. VISIBLE AND INFRARED SATELLITE SHOWS LAYERED CLOUDS ALONG THE MIDLEVEL JET STEAM MOVING ACROSS THE EASTERN AND CENTRAL PORTIONS OF THE STATE. ISOLATED EMBEDDED THUNDERSTORMS ARE ALSO PRESENT WITHIN THE EASTERN PORTION OF THE LAYERED CLOUD BAND...AND IS AFFECTING THE BIG ISLAND AND MAUI LATE THIS AFTERNOON. AFTERNOON SOUNDINGS SHOW PRECIPITABLE WATER VALUES OF 0.95 INCHES IN LIHUE TO 1.46 INCHES AT HILO INDICATIVE OF THE CONSIDERABLY DRIER AIRMASS HAS PUSHED INTO KAUAI AND SPREADING TOWARDS OAHU. 500 MB TEMPERATURES WERE -15 C ON THE LIHUE SOUNDING AND -13 C ON THE HILO SOUNDING. THE COLD POOL ALOFT ASSOCIATED WITH THE UPPER LEVEL TROUGH IS WHAT IS MAKING THE ATMOSPHERE UNSTABLE ACROSS THE EASTERN PORTION OF THE STATE...WHILE THE PLENTIFUL MOISTURE NEAR THE TROUGH IS ALLOWING FOR HEAVY RAIN AND THUNDERSTORMS TO OCCUR OVER MAUI AND THE BIG ISLAND. NORTHEAST TRADE WINDS CONTINUE TO PUSH EASTWARD ACROSS THE STATE WHICH IS ASSOCIATED WITH A 1026 MB HIGH CENTERED NORTHWEST OF THE STATE. WINDS HAVE STRENGTHENED ON MAUI...AND WILL SPREAD TO THE BIG ISLAND TONIGHT. THE UPPER TROUGH WILL PERSIST NORTHWEST OF THE STATE INTO EARLY NEXT WEEK. THE TROUGH WILL CONTINUE TO PUSH THE DEEP LAYERED MOISTURE UP OVER THE BIG ISLAND. THIS UPPER TROUGH IS CAUSING THE STRONG WINDS ALOFT AND PROMPTED A WIND ADVISORY ON THE BIG ISLAND SUMMITS. IN ADDITION...THE DEEP MOISTURE IS REACHING FAR ENOUGH UP TO PRODUCE SNOWFALL...ICING AND FREEZING FOG ON MAUNA KEA AND MAUNA LOA LIKELY THROUGH AT LEAST SUNDAY NIGHT. A WINTER WEATHER ADVISORY REMAINS IN EFFECT FOR THESE AREAS THROUGH SUNDAY NIGHT. AT THE LOW LEVELS...TRADE WINDS WILL DIRECT MOISTURE ONTO THE WINDWARD SLOPES FOR ALL ISLANDS. THE ABUNDANT MOISTURE NEAR THE BIG ISLAND WILL KEEP THE WINDWARD PORTION OF THAT ISLAND THE WETTEST. A WET AND BREEZY TRADE WIND PATTERN WILL LIKELY DEVELOP STATEWIDE BY SUNDAY NIGHT AND MONDAY...THEN PERSIST THROUGH AT LEAST THE MIDDLE OF NEXT WEEK. A LINGERING MID/UPPER LEVEL TROUGH OVERHEAD WILL MAINTAIN SOMEWHAT UNSTABLE CONDITIONS ALOFT WITH THE USUAL MID LEVEL INVERSION LIKELY REMAINING WEAK OR ABSENT. MODEL CONSENSUS SHOWS PLENTY OF AVAILABLE LOW LEVEL MOISTURE BEING PUSHED AGAINST THE TERRAIN BY BRISK TRADE WIND FLOW. ECMWF AND GFS MODELS DIVERGE SOMEWHAT TOWARD THE END OF NEXT WEEK. BOTH MODELS KEEP STRONG TRADES IN PLACE...BUT THE ECMWF PUSHES A DRIER AIRMASS SOUTH ACROSS THE STATE WHILE THE GFS KEEPS MOISTURE FURTHER NORTH IN RESPONSE TO A DEVELOPING LOW PRESSURE AREA NEAR THE DATELINE. && .AVIATION... A SURFACE TROUGH NEAR THE BIG ISLAND AND AN ELONGATED UPPER LEVEL TROUGH OVER ISLANDS ARE ACTING TO PRODUCE UNSETTLED WEATHER...MAINLY OVER MAUI AND THE BIG ISLAND. THUNDERSTORM ACTIVITY HAS BECOME MORE ISOLATED...HOWEVER POTENTIAL REMAINS THROUGH THE NIGHT FOR AREAS OF MAUI AND THE BIG ISLAND. CLOUD TOPS TO FL350 AND IFR CONDITIONS CAN BE EXPECTED IN THUNDERSTORMS. AIRMET SIERRA FOR MOUNTAIN OBSCURATION REMAINS POSTED FOR N THRU E FACING SECTIONS OF THE BIG ISLAND AND MAUI. ALONG WINDWARD AREAS OF THE THE SMALLER ISLANDS...PERIODS OF TEMPO MVFR ARE LIKELY. AIRMET TANGO IS POSTED FOR MODERATE TURB BETWEEN FL250 AND FL350 ASSOCIATED WITH A UPPER LEVEL JET MOVING OVER THE ISLANDS. THE LAYERED CLOUDS MOVING OVER WITH THE JET ARE THICK ENOUGH TO SUGGESTED TEMPO LIGHT ICING ABOVE 130. && .MARINE... A SURFACE TROUGH WITH A NORTH-TO-SOUTH AXIS IS LOCATED NEAR THE BIG ISLAND. THIS IS RESULTING IN GENTLE WINDS AROUND THE BIG ISLAND WITH STRENGTHENING NORTHEAST TRADE WINDS OVER THE SMALLER ISLANDS WHICH ARE UNDER THE INFLUENCE OF A HIGH PRESSURE SYSTEM NORTHWEST OF THE STATE. THESE WINDS WILL BUILD EASTWARD OVER THE BIG ISLAND TONIGHT. A SMALL CRAFT ADVISORY FOR STRONG WINDS HAS BEEN ISSUED BEGINNING SUNDAY MORNING FOR WATERS NEAR KAUAI...AND CHANNELS NEAR THE BIG ISLAND AND MAUI COUNTY. IN ADDITION...THE THREAT OF THUNDERSTORMS WILL CONTINUE OVER WATERS NEAR THE BUG ISLAND AND MAUI THROUGH THE WEEKEND. BREEZY TRADES APPEAR LIKELY TO CONTINUE THROUGH NEXT WEEK WITH THE POSSIBILITY OF EXPANDING THE SCA TO OTHER ZONES DURING THE SECOND HALF OF THE WEEK AS WINDS STRENGTHEN FURTHER. A NORTH NORTHWEST SWELL WILL BUILD ON SUNDAY...PRODUCING NORTH SHORE SURF AROUND THE ADVISORY LEVEL SUNDAY NIGHT AND MONDAY. SMALLER NORTH-NORTHWEST SWELLS ARE DUE NEXT WEEK. SEE THE COLLABORATIVE NEARSHORE SWELL AND WIND FORECAST /SRDHFO/ FOR MORE DETAILS. && .HFO WATCHES/WARNINGS/ADVISORIES... WINTER WEATHER ADVISORY UNTIL 6 AM HST MONDAY FOR BIG ISLAND SUMMITS. WIND ADVISORY UNTIL 6 PM HST SUNDAY FOR BIG ISLAND SUMMITS. SMALL CRAFT ADVISORY FROM 9 AM SUNDAY TO 9 AM HST MONDAY FOR KAUAI NORTHWEST WATERS-KAUAI LEEWARD WATERS-MAALAEA BAY-PAILOLO CHANNEL-ALENUIHAHA CHANNEL. && $$ UPDATE...WROE PREV DISCUSSION...FOSTER AVIATION...EATON MARINE...FOSTER/WROE Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office |
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